1. Field of the Invention
The present invention relates to a musical tone synthesizer suitable for simulating a brass instrument.
2. Description of the Related Art
A method for synthesizing a musical tone of an acoustic instrument by operating a model simulating the tone generating mechanism of the acoustic instrument is known. In particular, a closed loop structure model constituted by connecting a nonlinear amplification element for simulating the elastic characteristic of a reed and a bidirectional transmission circuit for simulating a resonator is known as a basic model of a brass instrument such as clarinet. In this type model, a backward or reflected wave signal is added to a signal outputted from the nonlinear amplification element, and then the resultant signal is supplied, as a forward or advancing wave signal, to the bidirectional transmission circuit.
Then, the forward wave signal is reflected at a terminal portion of the bidirectional transmission circuit, so that the reflected signal propagates on the bidirectional transmission circuit in the reverse direction. Thereafter, the reflected signal is added to the forward wave signal and fed back to the nonlinear amplification element (excitation circuit). As a result, the propagation of an air pressure wave on the brass instrument is simulated by a closed loop circuit composed of the nonlinear amplification circuit and the bidirectional transmission circuit.
Some acoustic brass instruments have holes for pitch control which are so called "tone holes". A model for simulating the brass instrument inclusive of the tone holes is also known. In this type model, signal processing circuits called "signal scattering junctions" (hereinafter merely called "junctions") are interposed between bidirectional transmission circuits correspondingly to the tone holes. The junctions respectively carry out arithmetic operations such as multiplying input signals from adjacent bidirectional transmission circuits by coefficients, so that the results of the arithmetic operations are respectively supplied to the adjacent bidirectional transmission circuits. In the arithmetic operations, multiplication coefficients and the like are respectively switched corresponding to the opening/closing conditions of the tone holes.
In this case, a signal fed back to the nonlinear amplification element is the sum of components turning back at the respective junctions. Further, as described above, multiplication coefficients for arithmetic operations at the respective junctions are switched corresponding to the opening/closing conditions of the tone holes, so that frequency characteristics of transmission in the bidirectional transmission circuit side seen from the nonlinear amplification element side are switched corresponding to the opened/closed conditions of the tone holes.
In the frequency characteristic of transmission, a plurality of peaks are formed as resonance frequencies composed of a fundamental frequency corresponding to the delay time which it takes for an output signal from a nonlinear amplification element to be propagated through the transmission circuit, to be reflected at a junction corresponding to an opened tone hole and be fed back to the nonlinear amplification element, and harmonic frequencies which are integral multiples of the fundamental frequency. This type of technique has been disclosed in U.S. Pat. No. 4,984,276.
The aforementioned technique is aimed to simulate a woodwind instrument. There is no model known for simulating a brass instrument (lip-reed instrument). In the brass instrument, various parameters for a musical tone are controlled by the lip condition of a player. The brass instrument has instability peculiar at the time of the rising of the musical tone. Further, the brass instrument has a characteristic in which the musical tone contains a lot of harmonic components. Because of these characteristics, a musical tone generated by an electronic musical instrument is inclined to be unnatural as brass instrument tones if these characteristics cannot be reflected on the musical tone.